High Resolution Dynamics Limb Sounder Post Launch Operation

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HIRDLS is one of four remote sounding instruments on the NASA Aura satellite which was launched into a near polar Earth orbit in July 2004. HIRDLS views the limb (horizon) of the earth, and by measuring the infra red radiation emitted by the atmosphere as the view scans up and down, it provides data which are then used to derive the vertical distributions of atmospheric species such as ozone and nitric acid, plus temperature and cloud/aerosol amounts, all at a vertical resolution of 1.0 to 1.5 km which is considerably better than previously. A profile is measured about every 15 secs which means that most of the Earth is covered every day. HIRDLS suffered a problem during launch, when a piece of protective plastic film tore and moved into the path of the optical beam, where it remains despite extensive attempts to dislodge it with the scan mirror. This delayed the start of scientific data acquisition, using the unobstructed view remaining, until January 2005, and necessitated extensive research and development of correction techniques, plus coding of new software, new onboard scanning sequences, and special in-flight tests. The data product validation was consequently delayed, but regular production is due to begin in late 2006. Apart from this problem, the instrument is working very well and delivering high quality measurements continuously. HIRDLS was designed, built and tested by a UK-US consortium, and funded by NASA and NERC in their respective countries. The consortium is also responsible for data analysis, data product validation, flight operations and UK data dissemination, the work now being conducted at Oxford University, the CCLRC Rutherford Appleton Laboratory, the University of Colorado and the US National Center for Atmospheric Research. The original UK funding was planned to extend until 18 months after launch. It was possible to stretch that, and this application covers the final three years of nominal life until July 2010. The funding supports several areas of work at Oxford University, namely: flight operations and instrument monitoring, calibration analysis, ground data processing algorithms, and data validation, together with the data handling and all the facilites needed to support these activities. The grant would fund the Rutherford Appleton Laboratory to undertake validation activities, and disseminate and archive the data via the British Atmospheric Data Centre. The validation work proposed includes comparison of instrument radiance data as well as HIRDLS geophysical products (e.g. profiles of temperature, ozone and other species) with independent measurements and data sets. Considerable interest has been shown by the UK scientific community, especially as the HIRDLS suite of data products is complementary to those measured by the other Aura instruments, so that together they form an important new data source.